Preparation of mixtures of rubbery butadiene styrene copolymer with hard resinous saturated copolymer of styrene and another unsaturated compound



Patented June 30, 1953 PREPARATION OF MIXTURES OF RUBBERY BUTADIENESTYRENE COPOLYMER WITH HARD RESKNOUS SATURATED GOPOLY- MER F STYBENE ANDANOTHER UNSAT- URATED COMPOUND Stuart A. Harrison, Stow, Ohio, andWalter E. Brown, Cambridge, Mass, assignors to The B. F. GoodrichCompany, New York, N. Y., a corporation ofNew York -No Drawing. Originalapplication May 23, 1946, Serial No. 671,897, now Patent No. 2,614,089,dated October 14, 1952. Divided and this application January 5,1052,Serial No. 272,504

1 Claim. 1

This invention relates to synthetic polymeric materials and to a methodof preparing the same, and is especially concerned with the preparationof polymeric materials in which a rubbery copolymer of a butadiene-1,3hydrocarbon and another polymerizable compound such as styrene isuniformly and intimately combined with a hard resinous saturatedoopolymer of a major proportion of styrene with a minor proportion of another unsaturated compound.

Robbery copolymers of a butadiene-l,3 hydrocarbon with styrene or itsequivalents, constitute a well known class of materials. Such materials(often called butadiene styrene synthetic rubbers) are characterizedchemically by possessing long carbon chains containing a multiplicity ofintra-chain carbon to carbon double bonds, that is, they are highmolecular weight (a molecular weight generally above 50,000) linearpolymers with a high degree of aliphatic unsaturation (iodine numbersgenerally above about 50) and are characterized physically by aresemblance to natural rubber in that they are capable of beingconverted from an essentially plastic workable condition to a highlyelastic condition by vulcanization, as by heating with sulfur.

Although such butadiene styrene synthetic rubbers resemble naturalrubber in many respects and are even superior thereto in certainrespects, they also possess an outstanding disadvantage as compared tonatural rubber. This disadvantage resides in the fact that they aregenerally much weaker and much less elastic when vulcanized in a puregum recipe (that is, a recipe which includes the rubbery material andvulcanizing ingredients but is free from significant amounts of othercompounding ingredients such as pigments, fillers, softeners, etc.) thanis natural rubber. For example, pure gum vulcanizates of natural rubberpossess a tensile strength ranging from 2,000 to 3,000 lbs/sq. in. ormore and are highly elastic, whereas pure gum vulcanizates of suchsynthetic rubbers possess tensile strengths generally less than 1,000lbs/sq. in; and often as low as 200 to 500 lbs/sq. in., and are notnearly so elastic. As a result, such synthetic rubbers must becompounded with carbon black (which remarkably reinforces the syntheticrubber, to an extent even greater than it does with natural rubber) toattain suflicient strength. to be useful, even though this isundesirable in many instances because of the black coloration and theincrease stiifness of the composition. I

Another class of polymeric materials, quite dif ferent in propertiesfrom the rubbery butadiene- 2 1,3 styrene copolymer's, are the hard,solid, resinous, saturated copolymers of a major proportion of styrenewith a minor proportion of copolymerizable monomer. These materials arealso high molecular weight polymers (molecular weight generally above50,000) containing long carbon chains, but they differ from the rubberycopolymers in that these chains are substantially saturated (the doublebonds of the monomer disappearing on. polymerization), and as a resultthe polymer possesses an iodine number of zero or thereabouts. Inphysical properties these materials also differ from rubbery materialssince they are hard and stiff at ordinary temperatures (having a Brinellhardness number in the unplasticized condition within the range of about10 to as measured on the Brinell apparatus using a 2.5 mm. ball with a25 kg. load) they are not appreciably elastic unless mixed withplasticizers; and they are not vulcanizable in the manner of naturalrubber. Moreover, they are thermoplastic whereas the rubbery copolymersstiffen at elevated temperatures.

One of the principal objects of this invention is to provide a methodwhereby rubbery butadiene- 1,3 styrene copolymers and hard saturatedresin?- ous styrene copolymers may be intimately combined with oneanother.

A second principal object is to provide a new class of syntheticpolymeric materials, which are rubbery and vulcanizable in nature, andwhich resemble natural rubber, rather than butadiene styrene syntheticrubber, in that they may be vulcanized in a pure gum recipe to producestrong snappy vulcanizates having a tensile strength above 1,000 lbs/sq.in., yet are far superior to natural rubber in resistance to oxidation,to chemicals and to other deteriorating influences.

Numerous other objects will be apparent hereinafter.

The first of the principal objects is attained by the method of thisinvention, which method comprises the steps of emulsifying a monomericmixture polymerizable in aqueous emulsion to form an unsaturated rubberycopolymer, and comprising a butadiene-L3 hydrocarbon and acopolymerizable compound such as styrene, in an aqueous emulsifyingmedium containing dispersed solid particles of a hard saturated resinousstyrene copolymer, and then polymerizing the said monomeric-materialwhile so emulsified. A most convenient way of proceeding is to poly'merize the mixture of butadiene-1,3 hydrocarbon and copolymerizablecompound in aqueous emulsion in the usual manner except that thepolymerization is carried out in the presence of a previously preparedaqueous dispersion or latex of the saturated resinous styrene copolymer.When practicing this method (sometimes referred to hereinafter for sakeof brevity as seeding the emulsion copolymerization forming a butadienestyrene copolymer with hard saturated resinous styrene copolymer), ithas been found that formation of rubbery copolymer occurs on thesurfaces of the particles of saturated resinous polymer to produce anaqueous dispersion in which the rubbery copolymer and the saturatedresin are present in the same individual particles. As a result,coagulation of the dispersion produces a polymeric material in which therubbery copolymer and the saturated resinous copolymer are uniformly andintimately combined, regardless of whether they are soluble in oneanother.

When the hard saturated resinous styrene copolymer is present in aproportion less than that of the rubbery copolymer, the second of theabove-stated objects is attained. For in this instance it has been foundthat the aqueous dispersion obtained by the polymerization consists ofparticles containing a core of the hard saturated resinous styrenecopolymer surrounded by a covering of vulcanizable rubbery copolymer,and that coagulation of this dispersion yields a rubbery vulcanizablepolymeric material comprising small discrete particles of hard saturatedresin evenly and intimately dispersed or embedded in a continuous phaseof the rubbery copolymer. Such copolymeric materials closely resemblenatural rubber in that they are strong and elastic, yet soft andflexible, when vulcanized in a pure gum recipe. They are quite useful inthe production of many articles customarily made from pure gum rubbercompounds such as nursing nipples, rubber thread, stationers bands,surgical goods, etc., which are superior to those made from butadienestyrene synthetic rubber because of a much greater strength andelasticity and are superior to those made from natural rubber because ofa greater resistance to various deteriorating influences. Additionally,these polymeric materials may be compounded with fillers, pigments, etc.and vulcanized to produce improved compositions useful for the samemultifarious purposes as are other rubbery materials, such compoundedmaterials being particularly useful for applications where it isundesirable to use carbon black as in producing white and brightlycolored compositions and in electrical insulation.

The practice of the invention in preferred embodiments may beillustrated by the following specific examples in which all parts are byweight.

EXAMPLE Seeding emulsion copolymerzaation of butadiene-1,3 and styrenedivinyl benzene copolymer with later of styrene resin In this example amixture of 75 parts of butadiene-1,3 and 25 parts of styrene isemulsified with '75 parts of a 5% aqueous soap solution, 0.3 part ofpotassium persulfate, 05 part of n-dodecyl inercaptan and with a latexof saturated styrene resinous copolymer containing 24.8 parts ofdispersed resinous copolymer and sufiicient soap solution to make atotal of 180 parts of water. The styrene copolymer latex used contains ahard benzene-insoluble copolymer of styrene and divinyl benzene, and isprepared by the poly merization in aqueous emulsion in the presence ofsoap and potassium persulfate of a monomer c 4 mixture consisting of 95%monomeric styrene and 5% divinyl benzene. The emulsion containing themonomeric butadiene-1,3 and styrene and the styrene divinyl benzenecopolymer particles is then agitated at 50 C. for about 15 hours,whereupon about 80% of the butadiene-1,3 and styrene is polymerized uponthe particles of styrene divinyl benzene copolymer. The resultingdispersion is coagulated to yield polymeric material comprising 31 partsof resinous styrene divinyl benzene copolymer for each 100 parts ofrubbery butadiene-1,3 styrene copolymer. The

polymeric material is then compounded in a pure gum recipe with 10 partsof litharge, 5 parts of zinc oxide, 5 parts of coal tar and 2 parts ofsulfur for each 100 parts of butadiene styrene copolymer present, andvulcanized for 45 minutes at 307 F. The physical properties of thevulcanized polymeric material is as follows:

Tensile strength lbs/sq. in 2600 Ultimate elongation per cent 650Modulus at 300% elongation lbs./sq. in 2500 It is seen that the resinousstyrene divinyl benzene copolymer increases the tensile strength andelasticity of the rubbery copolymer.

Results substantially equivalent to those set forth in the example aresecured by substituting for the specific styrene copolymer resin latexused, other latices of hard saturated resinous polymers prepared by thepolymerization in aqueous emulsion of a major proportion up to 95% byweight of styrene or other alkenyl substituted aromatic compounds of theformula wherein Ar is an aromatic radical having its connecting valenceon a ring carbon atom and R is hydrogen or alkyl, such as alpha-methylstyrene, p-methyl styrene, dichloro styrene, p-cyano styrene, p-methoxystyrene, vinyl naphthalene or the like, with lesser amounts of othercompounds copolymerizable therewith to yield hard saturated resinsincluding monomers containing a single olefinic double bond such asvinyl chloride, vinylidene chloride, methyl aorylate, methylmethacrylate, acrylonitrile and the like and also monomers containingtwo or more double bonds which are not conjugated such as divinylbenzene, dimethallyl, diallyl maletate, diallyl phthalate, allylcinnamate, trimethallyl phosphate, the dicinnamate ofl,4-dioxanediol-2,3,2-chloroa1lyl crotonate, allyl methacrylate, diallylketone and the like.

A particularly useful hard saturated resinous styrene copolymer inaddition to that used in the example is a latex containing about 30% byweight of small particles of hard resinous copolymer of about 80- partsof styrene and 20 parts of acrylonitrile preparable, for example, byemulsifying 80 parts of monomeric styrene and 20 parts of acrylonitrilewith 0.35 part of triisobutyl mercaptan as a polymerization modifier,and 0.2 part of p-methoxy-phenyl-diazothio-beta-naphthyl ether as apolymerization promoter in 300 parts of water containing 5 parts offatty acid I soap as emulsifying agent and 0.3 part of potassiumferricyanide as a polymerization catalyst and then polymerizing theemulsified monomers at 50 C. for 8 hours.

In the examples the monomeric mixture of butadiene-1,3 hydrocarbon andcopolymerizable compound which is polymerized to form a rubberycopolymer, has been a mixture of butadiene.-l,3

R AI(IJ=CHQ wherein Ar is an aromatic radical having its connectingvalence on a ring carbon atom and R is hydrogen or alkyl.

It is preferred that the saturated resinous styrene copolymer beprepared by polymerization in aqueous emulsion and that the dispersionor latex obtained be utilized to supply the resin, and it is alsopreferred that the particles of resin in the latex be no greater thanabout 0.4 micron in average diameter, and more preferably less thanabout 0.1 micron in average diameter, but other procedures for supplyingthe resin in dispersed form are also included. It is also preferred thatthe resin possess a Brinell hardnes number within the range of about to50 when measured on the Brinell apparatus using a 2.5 mm. ball with a 25kg. load, as do the resins used in the specific examples.

The precise proportion of hard saturated resinous styrene copolymeremployed in producing the polymeric products of the invention may bevaried throughout the range of 1 to 100 parts of resin for each 100parts of rubbery copolymer produced in the polymerization, and in eachinstance a rubbery vulcanizable polymeric material of considerablyhigher tensile strength than the rubbery copolymer alone is obtained.However, polymeric materials most useful for most purposes are securedwhen the proportion of hard saturated resin is from about 5 to 80 parts,more preferably from about to 60 parts, to each 100 parts of rubberycopolymer, since such polymeric materials when vulcanized give strongsnappy pure gum vulcanizates resembling those obtainable from naturalrubber. When the proportion of resin is increased to about 80 to 100parts for each 100 parts of rubbery copolymer, the polymeric materialsare still capable of vulcanization but are somewhat stiffer and morelike leather when vulcanized.

In addition to the above-discussed modifications and variations in thenature and proportions of essential materials used in practicing theinvention, other modifications and variations from the specific examplesare also possible. Thus, in polymerizing the monomer mixture containingbutadiene-1,3 hydrocarbon and styrene in aqueous emulsion in thepresence of a dispersion of the resin, use may be made of any of thevarious emulsifying agents, polymerization catalysts,

polymerization modifiers, etc. commonly employed in the polymerizationof butadiene-1,3 hydrocarbon containing mixtures in aqueous emulsion.The conditions of polymerization such as time and temperature and degreeof agitation may also be varied in accordance with establishedprocedures. Similar variations may be made in the polymerization to formthe hard saturated resin if it is formed by previous polymerization inaqueous emulsion.

The products of the polymerizations described are first obtained in theform of an aqueous dispersion or latex. These latices may be used assuch or they may be coagulated by any of the methods well known to theart, to yield the polymeric product in solid form. At this stage, thepolymeric products of this invention comprise a continuous phase ofrubbery copolymer in which there is dispersed small discrete particlesof hard saturated resin. Compounding ingredients such as softeners,plasticizers, pigments, fillers, colors, stabilizing agents,antioxidants, vulcanizing ingredients, etc. may be added to thedispersion before coagulation or to the solid polymeric products aftercoagulation in the manner well known to the art, if desired, it beingunderstood that the presence or absence of such materials will dependprimarily upon the use to be made of the finished product and is in noway critical in this invention.

It will be apparent from the above description that the invention is notlimited to the specific embodiments set forth, but only as required bythe spirit and scope of the appended claim.

This application is a division of copending application Serial No.671,897, filed May 23, 1946, now Patent No. 2,614,089.

We claim:

The method of preparing a resin-rubber mixture which comprisesincorporating in a binary styrene-acrylonitrile copolymer syntheticresin latex, the synthetic resin particles of which have a majorproportion up to 95 by weight of styrene component, a mixture ofbutadiene and styrene, the butadiene content of said mixture being 30-90by weight and the styrene content of said mixture being correspondinglyto 10% by Weight, subjecting the same to polymerizing conditions andcontinuing the polymerization until the butadiene-styrene copolymersynthetic rubber is to 50 of the thus formed resin-rubber mixture, andcoagulating and separating the thus formed mixture of synthetic resinand synthetic rubber from the aqueous medium.

STUART A. HARRISON. WALTER E- BROWN.

Soday Sept. 23, 1941 Guss et a1 Nov. 13, 1945 OTHER REFERENCES Kolthofiet 91., Rubber Chem. and Tech, Apr. 1947.

B1out et al., Monomers, published by Interscience Publishers, N. Y.1949, Styrene, pgs. 7-16.

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